1. Field of the Invention
This invention relates to devices that cut underwater lines, weeds, nets and the like and more particularly to shearing cutters that include a blade rotating with the shaft and propeller of a vessel that cooperates with a blade mounted on a non-rotating portion of a vessel adjacent the shaft with means for controlling the distance between rotating and non-rotating blades.
2. Description of the Prior Art
U.S. Pat. Nos. 4,447,215; 4,507,091, 4,544,363 and 4,801,281 have been issued to the inventor for propeller protecting devices that carry both a rotary cutter blade assembly and a stationary blade assembly on the rotating shaft or propellers of a boat. The rotary cutter blade assembly is fixedly connected to the rotating part and the stationary blade assembly is rotatably held in a fixed axial position relative to the rotating blades by bearing means and a flexible connection to the non-rotating part of the boat such as the strut or propeller shaft housing.
This bearing means is a source of wear, vibration and noise since it is continuously exposed to underwater debris, abrasive sand and fouling by marine organisms. Maintenance of the bearing is a minor problem for small boats that are frequently hauled out of the water. However, large commercial vessels that are in almost constant operation for prolonged periods are confronted with serious expense if the bearing must be serviced.
When a propeller is pushing a vessel forward in the water, the propeller and shaft exert a great forward force on the hull on a line coincident with the long axis of the shaft. This tends to move the shaft forward into the shaft housing. When in reverse, the axial movement is in the opposite direction. Thrust bearings take up the force and limit this axial movement. Temperature changes in the shaft also cause axial movement. When both the rotating and stationary blade assemblies are mounted at a common point on the shaft, the axial movement of the shaft does not effect the spacing between the two assemblies. However, when the rotating blade assembly is mounted on the shaft and the stationary blade assembly is mounted on the hull, then some mechanism must be provided to maintain a spacing between the blades close enough for shearing despite these axial movements. That mechanism must respond slowly to the axial movement to avoid moving away abruptly at the moment the moving blade and the stationary blade engage a foreign object for shearing action. A secondary mechanism that tends to bring the blades together at the moment of engaging the foreign object would further enhance the shearing action.